The following account of the prior art relates to one of the areas of application of the present invention, hearing aids.
In hearing aids, acoustic feedback from the receiver to the microphone(s) may give rise to signal degradations or even howl if not dealt with. Often, to reduce this problem, an adaptive feedback cancelling algorithm is used, which estimates the feedback channel transfer function using adaptive filtering techniques such as LMS, RLS, etc. The actual feedback transfer function is determined by physical parameters such as relative location of the microphone and receiver, jaw movements, actions by the hearing aid user (telephone-to-ear, hug, etc.), and generally distance to reflecting objects, walls, etc. When the actual feedback transfer function changes slowly, and the gain applied in the hearing aid is not too high, standard adaptive schemes like LMS are adequate. However, in practice, this is often not the case, and the standard adaptive algorithms fail to track the changing feedback channel.